There is conventionally known a developing cartridge including a developing roller. The developing cartridge is attachable to and detachable from an image forming apparatus.
Prior art discloses a developing cartridge including a developing roller and an electrode electrically connected to the developing roller. The electrode includes a shaft contactable with a power supply portion of the image forming apparatus. The developing cartridge further includes a gear rotatable about the shaft, and a protrusion positioned at the gear. The protrusion is circularly movable together with the rotation of the gear, and is in contact with an actuator of the image forming apparatus. The actuator moves by the contact with the protrusion. The image forming apparatus detects the movement of the actuator to determine specification of the developing cartridge.